In a fuel cell system, the fuel gas represented by hydrogen gas and the oxidant gas represented by air are supplied to a fuel cell, and electric power is generated by the generation reaction (water generation reaction) of the fuel gas and the oxidant gas. As the fuel cell, various types of fuel cells have been developed. Among them, a polymer electrolyte fuel cell (PEFC) that has no problems with dissipation or retention of an electrolyte, having advantages that it starts up at room temperature and that warm-up time is extremely short, attracts a special attention. In order to obtain high voltage, stacked PEFCs are adopted in movable bodies such as automobiles.
In this polymer electrolyte fuel cell, a polymer electrolyte layer conducts protons in the reaction between fuel gas and oxidant gas. Therefore, in order to efficiently maintain a generation reaction, it is necessary to monitor the wet condition or temperature condition of the polymer electrolyte layer, and to control it in an appropriate state.
In order to perform such control, for example, Patent Document 1 suggests a fuel cell system and method for measuring the temperature, humidity, and flow rate of the inflow gas to a fuel cell and the exhaust gas from the fuel cell to calculate the water balance with respect to the fuel cell, performing comparison with the generated water amount calculated from the electric power of the fuel cell to control the flow rate of the inflow gas, and controlling the amount of water remaining inside the fuel cell to within a proper level in the polymer electrolyte layer.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-192973